Ok. I have an alpine MRV-T757 amp that was my brothers and I do not have any of the literature on it. I looked around the internet and this is what I can find on it:

Alpine MRV-T757

Key Features
• Max Power (EIAJ) 225Wx2 (4ohm; Stereo) 750Wx1 (Bridged 4ohm
• 12V RMS Continuous Power 4ohm; Stereo (0.08% THD) 75Wx2 2ohm; Stereo (0.3% THD) 150x2 Bridged 4ohm; (0.3% THD) 300x1
• 14.4V RMS Continuous Power 4ohm; Stereo (0.08% THD) 100Wx2 2ohm; Stereo (0.3% THD) 200x2 Bridged 4ohm; (0.3% THD) 400x1
• S/N Ratio 105dBA
• Frequency Response 10-50kHz
• 24dB LP/12dB HP Crossover (30-200Hz)
•1-Band Parametric EQ
(30-200Hz)
• Subsonic Filter (15Hz)
• Fan Cooled
• Extra Large Gold Plated Terminals with Wire Insert Capability
• Top Panel Power LED
• 4 Volt Input Capability
• Continuously Adjustable Crossovers
• DC Straight, STAR Topology & Duo-B Circuitry
• DC-DC/PWM MOSFET Power Supply


From this information could someone tell me what a good sub option would be? I will just have one 10" and not sure exactly what all this means. Does the amp produce 200x2 rms @ 4 ohms and 400x1 rms @ 4 ohms? It gives numbers for both 2 and 4 ohms but Im really a newbie to this and not sure what it all means. If someone could help explain some of this to me and what some good options for a sub are, I would be very grateful. Thanks!!!

 

What you have is a pretty decent amp. It should be fine for a nice 10" sub. As far as the ratings, I would tend to think the 12V figures are more realistic for most installations. In regards to the ohm ratings, most amps will produce more power(sometimes double) into 2 ohms than into 4. So it can be beneficial in some ways to wire speakers to get a 2 ohm result. This is when using the amp in 2 channel mode. But bear in mind that even if you double your amp's output, the sound level will NOT double. You may see an increase of 3db. To double sound level would require something in the neighborhood of 10 times the power. When you bridge this particular amp, different rules apply. A bridged 2 channel amp that is "safe" to use into 2 ohms in 2 channel mode can only be safely used into 4 ohms in this bridged mode. You are actually using part of each channel, and the amp works differently than it does in 2 channel. (If you had a true mono amp made specifically for sub use, this wouldn't apply.) So I would recommend you bridge the amp and use a single 10" sub that has a single 4 ohm voice coil that will handle about 300-400 watts RMS(continuous). Just my opinion.

 

Thanks a lot.

Right now I have the amp hooked up to a rockford fosgate 10" with just one channel going to it. Im assuming this is giving it about 75 W rms. I built the box just for the sub and the air space is right but the speaker seems to distort at some points. I dont think the gain is turned up very high on the amp and this doesnt seem right to me. Any ideas?

I would like to get a nice sub and bridge the amp and put on it but I dont want to run into the distortion problem again but maybe the amp just needs to be adjusted by someone who knows what there doing?

Last, most amps I have seen have some kind of wiring diagram telling how to bridge the amp. Is there a general way to bridge the amp into one channel at 4 ohms and if so how?

Thank you very much for any tips as anything is very helpful!!!

 

Makes sure that you have the amp bridged. You will use CH1 (+) and CH3 (-) on that amp or the equivalent of left + right -. This will ensure you are getting all the power out of the amp that is available. Also be sure you are using the x-over built in the amp to filter out the highs. Oh this is bridged mode so be sure you do not drop the impedance below 4 ohm since the amp in bridged mode effectively will half the impedance.

 

Bridged mode does NOT halve the impedance. That is a physical impossibility. If you have a 2 or 4 ohm configuration, bridging your amp can in NO way change this fact. This is a common statement that you will even hear shop personnel come across with, and it is blatantly INCORRECT. People who are just learning don't need to hear these kinds of things because then they pass them on to other newbies, when, in fact, they don't know what they are even saying. They say it because someone else told them. When you bridge a 2 channel amp, you are using part of each channel, which increases voltage and current. It is SIMILAR to the effect a 2 ohm load would have on the amp in 2 channel because of the way the amp has to operate in this bridged mode. That's why a 2 channel amp "safe" to 2 ohms can only be used into 4 ohms when bridged. Not because impedance is halved.

 

This should be required reading for those new to the car audio world. This tutorial sure helped me out a heck of a lot, and it explains terms simply, and yet gets technical, too, if you want/need it.

A 4-ohm speaker's impedence is 4 ohms whether you plug it into your head unit, bridged amp, a wall outlet, or your toaster...

That's the way the passage in the above linked tutorial simply put it. I recommend checking it out!

 

OK, I see that some want to get into a debate talking way above the head of the original person asking the question.

However, do we really want to get into power equations, circuit topology, AC/DC theory with someone asking how to wire an amp? No, I don't think so.

Did I say that the ohm load will be physically altered? NO.

What I stated was the load will be EFFECTIVELY halved not physically halved. I understand that the physical charateristics of a speaker or combination thereof cannot be altered without re-winding the voice coil or changing the wiring configuration etc..

However, since an industry standard has been adopted to classify amps as 2 ohm stable they merely need to know that 4-ohm bridged serves the same purpose of loading the amp in a 2-ohm stereo configuration. Which in the first post in reply to the question did in fact state that point. I was merely backing up that original post with confirmation on your behalf. If anyone would like to get into any advanced topic discussion I would love to delve deeper into the subjects of phase inversion, circuit classification, reactance theory, or any other subject matter involving the physics of electricity and how they are applied.

 

Sorry for the rant there. I just hate being mis-quoted or having assumptions placed on my statements. I did notice that one of the questions went un-answered.


Does the amp produce 200x2 rms @ 4 ohms and 400x1 rms @ 4 ohms? The amp will yield those power ratings when wired either bridged or stereo configuration individually, not simultaneously.

 

No problem for your rant

I think it's good to get stuff out on the table, for more than a few of us, all this is an educational process to be sure.

We can fix our mistakes, and enjoy the results...

 

[QUOTE]Originally posted by cgorris
[B]Sorry for the rant there. I just hate being mis-quoted or having assumptions placed on my statements. I did notice that one of the questions went un-answered.

Sorry for my rant, but it sounds as though you are the one making assumptions. You ASSUMED that an explanation would be "over the head" of the original poster. You could make a simple, easy to understand explanation. How else can a newbie BEGIN to learn? No offense intended, but that sounds arrogant on your part. Just my opinion. I wasn't trying to mis-quote or assume anything when I responded with my post. I just saw the opportunity to point out a common misrepresentation of facts. If you are as knowledgeable in these technical aspects of car audio as your language would lead us to believe, then I would think it would be important to you to teach the newbies with accuracy. Any mention of EFFECTIVELY "halving the impedance" is WRONG, plain and simple.

 

CGORRIS... there's no need to start TAUNTING your knowledge. Many of us here know you have a good knowledge of the subject. I for one did not understand your statement and just didn't pay much attention to it cuz I'm sure you knew what you meant.. I just didn't understand how you worded it.

Another point I'd like to make concerning the "going over the head of the original poster". On another thread in Subwoofers.. a guy asks about how important the frequency response rating of the sub is and you start talking about Aperiodic Membrane enclosures... I thought that was a little over the head.

Not trying to start an argument with ya... just giving my rant-rebuttle. LOL

 

How about capacitive / inductive reactance ? I'd love to re-hash 2nd semester electronics. It's been 20 years or so...

Wow, you guys get wound up easy. If you don't calm down, you are gonna rupture your aperiodic membranes.

OK. All kidding aside. I have to comment on something I've observed here and other places:

People like to quote facts / figures / formulas / etc. right up until it goes against something they believe. Then, magically, the data goes out the window and it becomes a matter of being able to hear the difference because of a "trained ear" or whatever.

Examples would be the "oxygen-free" cables, super-heavy speaker cables (for runs that are typically less than 15 feet !), capacitors, "special" RCA cables, etc. I laugh when I see the prices on some of that stuff. The sad part is people are parted with their hard earned cash, which would be much better spent on higher quality equipment, installation, etc.

All I can say is I have measured all of that stuff (and quite a few other items as well) with some VERY expensive HP audio analysis lab equipment. While the answers don't always prove popular with everyone, I can prove that you cannot hear the difference between 16 gauge speaker cable and Monster Cable, when both are installed properly in an automobile for example.

These are some of the reasons it is such a shame that audio equipment manufacturers no longer adhere to meaningful standards, such as those the FTC implemented so many years ago. Those standards were developed to stop the kind of crap that goes on today with audio gear. As they like to say in the lab: The oscilliscope doesn't lie or care how expensive the component is - only the owner does.

Oh well, people like what they like and they believe what they believe.

Let the flaming begin (or continue) !!!!

 

Well if I made an assumption or it appeared that I did I appologize. I don't mind being corrected or having comments added to or clarified. My comments here are only meant with best interest and I know I sometimes have the ability to come off as arrogant at times although that is really not the intent (let's just call that a personality flaw). That is why I did after the rant appologize for it because I realized I sounded like a pompus a$$. I know that there are many out there with as much knowledge and even more knowledge than myself. It has been proven many times in the past and I am sure will prove to be that way in the future. After years of experience and school I still learn something new almost every day.

<snip>Wow, you guys get wound up easy. If you don't calm down, you are gonna rupture your aperiodic membranes. <snip>

LOL! Good slam B-MAN

Point taken TEK2000! I just thought he may want to know benefits/drawbacks of other enclosures on that thread.

I will try to be better, I promise

 

Good deal, Chris. Your knowledge is evident and appreciated.

 

GOOD THREAD... went sour for a while there but now its coming back around in a joking sense. Sometimes what people say and what people actually mean can be misconstrued from person to person... an inherent problem with human communication.

I agree CGORRIS... if those OTHER types of enclosures, methods, ideas aren't brought up... no one would ever learn about them. So, even though the person who asked the question may not understand all that is replied... they at least have something to research further and something new to learn.. if they wish.

We should all just head out to Hooters.. have some hot wings and cold beer and all calm down.